The optimal operational conditions achieved during the fermentation of Escherichia coli MC1061 strain in a pilot plant (0.4 vvm, 215 rpm), are scaled-up for a production level of 200 1. using a constant volumetric oxygen transfer coefficient (K(L)a) and the volumetric airflow rate per volume unit (Q/V). The Wang and Cooney correlation where aeration efficiency, superficial air velocity and power consumption per volume unit, are correlated, and the scale-up criteria applied. enabled a yield of 30.1 +/- 5.6 mg/l of K99 to be obtained. (C) 2002 Elsevier Science Ltd. All rights reserved.